Method for fluorinating a compound comprising a halosulphonyl or dihalophosphonyl group

ABSTRACT

The invention relates to a fluorination process for producing fluorinated compounds. 
     The process consists in reacting a compound (I) corresponding to the formula 
                         
with an ionic fluoride of a monovalent cation. M represents H, an alkali metal, a quaternary phosphonium group or a quaternary ammonium group. Y represents SO 2  and m is 1, or else Y is PO and m is 2. Z represents CR 2 , N or P. R 1  represents an electron-withdrawing group which has a Hammet σ P  parameter of greater than 0.4. R 2  represents a carbonaceous and/or electron-withdrawing group. X represents a halogen other than a fluorine.
 
     The fluorinated compounds obtained are of use in particular as electrolytes in lithium batteries.

This application is filed under 35 USC 371, from PCT/FR01/04164, filedDec. 21, 2001.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a fluorination process for producingfluorinated compounds which can be used in particular as electrolyte.

2. Description of the Related Art

Lithium batteries, in which the anode is formed by a sheet of lithiummetal or by a lithium alloy and which operate by movement of lithiumions between the electrodes, have been widely studied. However, theirdevelopment has been impeded due to the fact that, during theirrecharging, deposition of lithium metal of dendritic nature occurs,which can lead to short-circuits, resulting in an explosion in thesystem. This risk has been eliminated by replacing the lithium orlithium alloy anode by an anode composed of a carbonaceous material inwhich the lithium ions can be reversibly inserted. This novel form oflithium batteries, known as “lithium-ion” batteries, is widely used inthe field of portable electronic equipment. The electrolyte of thesebatteries comprises at least one lithium salt in solution in an organicsolvent which can be a polar aprotic liquid solvent (for example,ethylene carbonate, propylene carbonate or a dialkyl carbonate)optionally supported by a porous plastic support, a polar polymer [forexample, a crosslinked poly(ethylene oxide)] or a liquid solvent gelledby a polymer. The lithium salt plays an important role in the operationof the battery. The most widely used salt is LiPF₆, which makes itpossible to obtain liquid electrolytes which have a conductivity ofgreater than 10⁻² S.cm⁻¹ at ambient temperature. However, it has alimited thermal stability, which results in the formation of LiF and ofHF, said HF leading to decomposition of the electrolyte which can resultin an explosion in the battery. The lithium salt ofbis(trifluoromethanesulfonyl)imide has been envisaged for replacingLiPF₆, but it exhibits the disadvantage of resulting in depassivation ofthe aluminum current collector of the cathode.

The use of imide salts or methane salts having FSO₂ or F₂POelectron-withdrawing groups was then studied (WO 95/26056). These saltsmake it possible to obtain electrolytes with a greater conductivity thantheir homologues comprising perfluoroalkyl groups instead of thefluorine atoms and they result in markedly lower corrosion of thealuminum collectors. The use of an imide salt or methane salt comprisingFSO₂ or F₂PO groups thus makes it possible to maintain the low level ofcorrosion observed with LiPF₆ while improving the thermal stability withrespect to that of LiPF₆.

Various processes for the preparation of imide salts or methane saltscomprising at least one FSO₂ or F₂PO group have been described. Forexample, bis(fluorosulfonyl)imide (FSO₂)₂NH can be prepared by reactionof fluorosulfonic acid FSO₃H with urea H₂NC(O)NH₂. The imide issubsequently isolated by treatment of the reaction mixture with NaCl indichloromethane, followed by distillation of the pure acid [Appel &Eisenhauer, Chem. Ber., 95, 246–8, 1962]. However, the toxicity and thecorrosive nature of FSO₃H constitute a major disadvantage.

Another process consists in reacting (ClSO₂)₂NH with AsF₃. The acid(FSO₂)₂NH is subsequently isolated by treating the reaction mixture withNaCl in dichloromethane [Ruff and Lustig, Inorg. Synth., 1968, 11,138–43]. The disadvantage of this process lies in particular in the highcost of AsF₃, in its toxicity and in the risk of contaminating thecompound obtained.

For the phosphoryl derivatives, a process for the preparation ofLiN(POF₂)₂ consists in reacting LiN(SiMe₃)₂ with POF₃. The removal ofvolatile Me₃SiF results directly in the expected product [Fluck andBeuerle, Z. Anorg. Allg. Chem., 412(1), 65–70, 1975]. The disadvantageof this process lies in the cost of the silylated derivative and the useof gaseous and toxic POF₃.

It is known to prepare a fluorinated compound from the correspondinghalogenated compound by a halogen exchange reaction using an ionichalide, such as, for example, KF or CsF, or an organic fluoride, such astetra(n-butyl)ammonium fluoride. The reaction is a nucleophilicsubstitution which preferably takes place in a polar aprotic solvent.The exchange reaction is promoted by the presence of a phase transfercatalyst chosen, for example, from quaternary ammonium salts, crownethers, pyridinium salts or quaternary phosphonium salts. This processhas been carried out with KF in particular to obtain monofluoroalkanes,α-fluoroesters, fluoroethers, acyl fluorides or sulfonyl fluoridesrespectively from the corresponding monohaloalkanes, α-haloesters,haloethers, acyl halides or sulfonyl halides [A. Basbour et al. in M.Stacy and co-editors, Advances in Fluorine Chemistry, Vol. 3,Butterworth, Washington D.C., 1963, pp. 181–250].

SUMMARY OF THE INVENTION

The inventors have now found that, surprisingly, the halogen/fluorineexchange process can be employed for the fluorination of variouscompounds comprising at least one halosulfonyl or dihalophosphoryl groupattached to an atom carrying at least one strongly electron-withdrawingsubstituent and optionally an acidic hydrogen.

The aim of the present invention is consequently to provide a processfor the fluorination of a compound comprising at least one halosulfonylor dihalophosphoryl group in which the halogen is other than a fluorineand at least one strongly electron-withdrawing group, for the purpose inparticular of the preparation of the corresponding compounds comprisingat least one fluorosulfonyl or difluorophosphoryl group.

The fluorination process according to the present invention consists inreacting, optionally in a solvent, a fluorinating agent with a compound(I) comprising a halosulfonyl or dihalophosphoryl substituent in whichthe halogen is other than a fluorine, wherein the fluorinating agent isan ionic fluoride of a monovalent caton and wherein the compound (I)corresponds to the following formula:

in which:

-   -   M represents H, an alkali metal, a quaternary phosphonium group        or a quaternary ammonium group;    -   Z represents CR², N or P;    -   Y represents SO₂ and m is 1, or else Y is PO and m is 2;    -   R¹ represents an electron-withdrawing group which has a Hammett        σp parameter of greater than 0.4;    -   R² represents a carbonaceous and/or electron-withdrawing group;    -   X represents a halogen other than a fluorine.

The process is particularly preferred for the compounds in which Zrepresents N.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The process is advantageously carried out at atmospheric pressure, at atemperature of less than 180° C. The temperature is preferably less than100° C., more particularly less than 80° C. An excessively slow reactionrate results from carrying out the process at a temperature belowambient temperature. The reaction medium can be heated by conventionalmeans. Heating can also be carried out using microwaves. Stirring thereaction medium or applying ultrasound is of use in replacing the activesurface of the reactants when they are in suspension.

The monovalent ionic fluoride can be an alkaline fluoride or a fluorideof a stable onium cation. Among alkali metals, it is advantageous to useK or Cs. Among onium cations, tetraalkylammonium, tetraalkylphosphoniumor dialkylsulfonium cations are preferred. Onium cations in which thealkyl radicals (which can be identical or different in an onium cation)have from 1 to 12, more particularly from 1 to 4, carbon atoms arepreferred. The abovementioned onium fluorides are advantageous becauseof their high solubility in organic solvents. They can therefore be usedalone or in combination with a less soluble ionic fluoride, for whichthey then act as charge transfer catalyst. When the cation M of thecompound (I) is al alkali metal or an onium as defined above for thefluoride, it is advantageous to use a fluoride of said cation M. The useof LiE or of NaF, although giving relatively slow reactions, isadvantageous when the fluorinated product obtained from the compound (I)is intended to be used as electrolyte. It is preferable to use an ionicfluoride having a high active surface.

The amount of ionic fluoride used with respect to the amount of compound(I) is preferably greater than stoichiometry. The ratio of the number ofmoles of fluoride to the number of halogen atoms to be exchanged of thecompound (I) is advantageously from 1.1 to 2. When the compound (I) isan imide [M is H in the formula (I)], said ratio is preferably greaterthan 2, more particularly greater than 3.

The process of the present invention is particularly suitable for thefluorination of compounds (I) in which M is H or an alkali metal, forexample chosen from Na, K, Li or Cs. When M is a quaternary ammonium ora quaternary phosphonium, it corresponds respectively to the formulaeN(R³R⁴R⁵R⁶) and P(R³R⁴R⁵R⁶) in which the various substituents R^(i) arechosen, independently of one another, from alkyl radicals preferablyhaving from 1 to 12, more particularly from 1 to 4, carbon atoms.

R¹ is an electron-withdrawing radical having a Hammett σp parameter ofgreater than 0.4. The radicals having a σp of greater than 0.5, moreparticularly of greater than 0.7, are particularly preferred.Preferably, the radical R¹ does not carry a positive charge at less than6 chain members from z. Mention may be made, as examples of radicals R¹,of:

-   -   X′SO₂— and (X′)₂PO— radicals in which the group X′ represents or        the two groups X′ represent, independently of one another:        -   a halogen,        -   a R⁷CF₂— radical in which R⁷ is a halogen other than F or a            carbonaceous radical preferably having at least 15 carbon            atoms;        -   a perhalogenated radical R_(F), preferably having a number            of carbon atoms of less than or equal to 15, corresponding            to the formula R⁸(CX″₂)p- in which:            -   each of the X″ groups represents, independently of one                another, F, C1 or a perfluoroalkyl radical having from 1                to 5 carbon atoms (preferably 2 carbon atoms), at least                one of the X″ groups being F, preferably carried by the                carbon connected to the sulfur, p being 1 or 2;            -   R⁸ is an electron-withdrawing atom or radical having a                σp of greater than 0 (preferably of greater than 0.1,                more particularly of greater than 0.2), the possible                functional groups of which are inert under the reaction                conditions, for example an F or a perfluoroalkyl having                at most 8 carbon atoms;    -   various radicals having a σ_(p) of greater than 0.4, mentioned        in particular in Advanced Organic Chemistry, 3^(rd) Ed., Gerry        March, p. 244, such as, for example, COOR′, COR′, SO₂R′, PO(R′)₂        or PO(OR′)₂ in which R′ is preferably an alkyl radical having        from 1 to 15 carbon atoms or an aryl radical having from 6 to 20        carbon atoms.

In a preferred embodiment, R¹— represents an X′SO₂— or (X′)₂PO— radicalas defined above.

The substituent R² represents a carbonaceous and/or electron-withdrawingradical. When R² is an electron-withdrawing radical, it isadvantageously chosen from the nitrile radical and the radicals definedabove for R¹. When R² is a carbonaceous group, it is preferably chosenfrom radicals having from 1 to 20 carbon atoms.

When the compound (I) is liquid at the reaction temperature and when theionic fluoride is soluble in said liquid compound, it is not essentialto add a solvent to the reaction medium.

When the two reactants are in the solid form, the reaction is carriedout in a liquid solvent. The solvent is aprotic when M is other than H.

When the solvation of the cation of the monovalent fluoride reactant isdesired, use is preferably made of a solvent having a donor number from10 to 30, preferably from 20 to 30. The donor number of a solventrepresents the value −ΔH, ΔH being the enthalpy (in kcal/mol) of theinteraction between the solvent and antimony pentachloride in a dilutedichloromethane solution [cf. Christian Reinhardt, Solvent and SolventEffects in Organic Chemistry, WCH, p. 19, 1988].

The solvents giving good results can in particular be amides, includingamides with a specific nature, such as tetrasubstituted ureas andmonosubstituted lactams. The amides are preferably substituted(disubstituted for ordinary amides). Mention may be made, for example,of pyrrolidone derivatives, such as N-methylpyrrolidone,N,N-dimethyl-formamide or N,N-dimethylacetamide. Another particularlyadvantageous category of solvents is composed of symmetrical orasymmetrical and open or closed ethers, including the variousderivatives of glycol ethers, such as glymes, for example diglyme. Thus,the most appropriate solvents, because of their cost and theirproperties, are advantageously chosen from ethers (in particular cyclicethers, such as THF, or polyfunctional ethers, such as glymes) or fromamides not having acidic hydrogen, such as DMF orN,N′-dialkyl-alkyleneureas, among which may be mentioned DMEU(N,N′-Di-MethylEthyleneUrea) or DMPU (N,N′-DiMethylPropyleneUrea).Mention may also be made of N-methylpyrrolidone and cyclic ureasperalkylated on the nitrogens.

In addition, the solvent can be nitromethane.

It may be advantageous to add a phase transfer catalyst to the reactionmedium, in order to improve the yield of the reaction. This addition isparticularly of use when the reaction is carried out in a nonpolar ornot very polar solvent. Mention may be made, as example of phasetransfer catalyst, of quaternary ammonium salts, crown ethers,pyridinium salts or quaternary phosphonium salts. The addition of aphase transfer catalyst is targeted at overcoming a relatively lowsolubility of the alkaline ionic fluoride used. A highly soluble ionicfluoride which can be used as fluorination reagent in the process of thepresent invention can be used as phase transfer catalyst when it iscombined with a fluoride reactant of low solubility. Mention may bemade, by way of example, of onium fluorides and cesium fluoride.

The compounds (I) can be prepared by processes of the prior art. Animide salt can be prepared by the action on the corresponding imide of asalt, the acid form of which is volatile under the reaction conditions.For example, the action of an alkaline hydride on an imide in a proticmedium makes it possible to obtain an anhydrous imide salt. It is alsopossible to react an alkylmetal compound, for example butyllithium, withan imide, in order to obtain the corresponding imide salt and an alkane,which is volatile if it is a lower alkane. In addition, it is possibleto obtain an imide salt from the corresponding imide by exchange with acarboxylate with a sufficiently low molecular weight for thecorresponding carboxylic acid to be volatile.

The present invention is illustrated by the following examples, towhich, however, it is not limited.

EXAMPLE 1

3.556 g (137.1 mM) of LiF were introduced into 5 ml of nitromethane in areactor and then the medium was stirred for 18 h in the presence ofglass beads. A solution of 4.907 g (0.22926 mM) ofbis(chlorosulfonyl)imide in 5 ml of nitromethane, corresponding to aLiF/imide molar ratio of approximately 6, was subsequently addeddropwise with stirring. The reaction was allowed to continue overnight.A solid residue separated by settling and the supernatant solution wasrecovered for NMR analysis of the fluorine.

The analysis showed the presence of fluorine singlets at variouschemical shifts and with different peak heights:

Chemical shift Peak height Entity 56.6 1 FSO₂NH₂ 50.8 78.4 (SO₂F)(SO₂Cl)NH 54.5 12.7 SO₂F 35.3 53.3 FSO₃ ⁻

After having continued the reaction for two weeks, different peakheights were obtained, the predominant compound being the desiredlithium bis(fluorosulfonyl)imide.

EXAMPLE 2

4.111 g (19.205 mM) of bis(chlorosulfonyl)imide were dissolved in 5 mlof nitromethane. 6.549 g (155.97 mM) of finely divided NaF were added at0° C. with continuous stirring. The NaF/imide molar ratio is of theorder of 8. The reaction mixture was allowed to rise to ambienttemperature and then was stirred in the presence of 3 glass beads for 60h. After separation by settling, fluorine NMR analysis of the clearsupernatant solution showed the presence of the desired product.

EXAMPLE 3

4.361 g (75.06 mM) of KF were suspended in 5 ml of nitromethane and thena solution of 3.176 g (14.84 mM) of bis(chlorosulfonyl)imide in 3 ml ofnitromethane was introduced with continuous stirring. The KF/imide molarratio is of the order of 5.

The reaction mixture heated up and the reactor was stirred with glassbeads for 14 h. 3.49 g (60.034 mM) of fresh KF were then added and themixture was stirred for a further 18 h. The solution became deep orange.After separating the solid particles by settling, the fluorine NMRanalysis was carried out, which showed that the predominant productexhibits a chemical shift (singlet) of 51.6 ppm and corresponds to theconversion of 99% of the starting product. The predominant productobtained is potassium bis(fluorosulfonyl)imide.

The procedure of this example was employed in three additional tests,using, instead of bis(chlorosulfonyl)imide, φSO₂NHSO₂Cl, CF₃SO₂NHSO₂Cland (φSO₂)₂CHSO₂Cl respectively, and the predominant formation of thefollowing compounds was observed: φSO₂NKSO₂F (from φSO₂NHSO₂Cl),CF₃SO₂NKSO₂F (from CF₃SO₂NHSO₂Cl) and (φSO₂)₂CKSO₂F from (φSO₂)₂CHSO₂Cl.

EXAMPLE 4

4.421 g (29.104 mM) of CsF were dispersed in 2 ml of nitromethane whilestirring with glass beads. A solution of 2.243 g (10.480 mM) ofbis(chlorosulfonyl)imide in 5 ml of nitromethane was added dropwise withstirring. The CsF/imide molar ratio is of the order of 3. After areaction time of 72 h, followed by stirring for 6 h, fluorine NMRanalysis of the supernatant liquid showed the following lines:

Chemical shift Peak height Entity 56.5 15.5 FSO₂NH₂ 52.1 48.3 (SO₂F)(SO₂Cl)N⁻ 51.9 225.6 [N(SO₂F)²]⁻

It thus emerges that 80% of the starting imide has been converted tobis(fluorosulfonyl)imide.

EXAMPLE 5

Bis(dichlorophosphoryl)imide was reacted with KF by a process analogousto that described in example 3. The conversion of the starting materialwith a yield of 90% and the predominant formation of potassiumbis(difluorophosphoryl)imide was noted.

Bis(dichlorophosphoryl)imide can be prepared according to the processdescribed by Riesel et al. [Riesel, Pfuetzner & Herrmann, Z. Chem.,23(9), 344–5, 1983].

1. A process for the fluorination of a compound (I) comprising reacting,optionally in a solvent, a fluorinating agent with said compound,wherein the fluorinating agent is an ionic fluoride of a monovalentcation and wherein the compound (I) corresponds to the followingformula:

in which: M represents H, an alkali metal; a quaternary phosphoniumgroup or a quaternary ammonium group; Z represents CR², N or P; Yrepresents SO₂ and m is 1, or Y is PO and m is 2; R¹ represents anelectron-withdrawing group which has a Hammett σ_(P) parameter ofgreater than 0.4; R² represents a carbonaceous and/orelectron-withdrawing group; X represents a halogen other than fluorine.2. The process as claimed in claim 1, which is carried out atatmospheric pressure.
 3. The process as claimed in claim 1, which iscarried out at a temperature between ambient and less than 180° C. 4.The process as claimed in claim 1, wherein the monovalent ionic fluorideis KF or CsF.
 5. The process as claimed in claim 1, wherein themonovalent ionic fluoride is tetraalkylammonium, tetraalkylphosphoniumor dialkylsulfonium fluoride.
 6. The process as claimed in claim 5,wherein the alkyl groups of the tetraalkylammonium,tetraalkylphosphonium or dialkylsulfonium fluoride have from 1 to 12carbon atoms.
 7. The process as claimed in claim 1, wherein the ratio ofthe number of moles of fluoride to the number of halogen atoms to beexchanged of the compound (I) is greater than
 1. 8. The process asclaimed in claim 7, wherein the ratio of the number of moles of fluorideto the number of halogen atoms to be exchanged of the compound (I) isfrom 1.1 to
 2. 9. The process as claimed in claim 7, wherein the ratioof the number of moles of fluoride to the number of halogen atoms to beexchanged of the compound (I) is greater than 2 when M is H.
 10. Theprocess as claimed in claim 1, wherein M represents H, an alkali metal,a quaternary ammonium N(R³R⁴R⁵R⁶) or a quaternary phosphoniumP(R³R⁴R⁵R⁶), the various substitutents R³, R⁴, R⁵, and R⁶ being chosen,independently of one another, from alkyl radicals preferably having from1 to 12 carbon atoms.
 11. The process as claimed in claim 1, wherein thecation M is identical to the cation of the monovalent fluoride.
 12. Theprocess as claimed in claim 1, wherein R¹ is an electron-withdrawinggroup having a Hammett 0p parameter of greater than 0.7.
 13. The processas claimed in claim 1, wherein R¹ and/or R² are an X′SO₂— or (X′)₂PO—radical in which X′ represents: a halogen, an R⁷CF₂— radical in which R⁷is a halogen other than F or a carbonaceous radical; a perhalogenatedradical R_(F), corresponding to the formula R⁸(CX″₂)_(p)— in which: eachof the X″ groups represents, independently of one another, F, Cl or aperfluoroalkyl radical having from 1 to 5 carbon atoms, at least one ofthe X″ groups being F, p being 1 or 2; R⁸ is an electron-withdrawingatom or radical having a σ_(P) of greater than 0, the possiblefunctional groups of which are inert under the reaction conditions. 14.The process as claimed in claim 13, wherein R⁷ is a carbonaceous radicalhaving at most 15 carbon atoms.
 15. The process as claimed in claim 13,wherein at least one of the X″ groups represents a perfluoroalkylradical having from 1 to 5 carbon atoms.
 16. The process as claimed inclaim 13, wherein at least one of the X″ groups is a F atom carried bythe carbon connected to the sulfur or the phosphorus.
 17. The process asclaimed in claim 13, wherein R⁸ is F or a perfluoroalkyl radical havingat most 8 carbon atoms.
 18. The process as claimed in claim 1, whereinR¹ represents a COOR′, COR′, SO₂R′, PO(R′)₂ or PR(OR′)₂ radical in whichR′ is an alkyl radical having from 1 to 15 carbon atoms or an arylradical having from 6 to 20 carbon atoms.
 19. The process as claimed inclaim 1, wherein R² is a nitrile or a carbonaceous radical having from 1to 20 carbon atoms.
 20. The process as claimed in claim 1, which iscarried out in an aprotic solvent.
 21. The process as claimed in claim1, wherein the solvent is nitromethane.
 22. The process as claimed inclaim 1, which is carried out in a solvent chosen from substituted orunsubstituted amides and symmetrical or asymmetrical and cyclic ornoncyclic ethers.
 23. The process as claimed in claim 1, wherein thereaction medium comprises a phase transfer catalyst.